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I've read cellphones can't play a sound in the 18-20kHz range. I don't know whether that is true or not. I saw this site this morning about high school kids using a tone adults can't hear due to unavoidable hearing loss that begins at age 20 called presbycusis. I did an experiment a moment ago using the tone in question.

1. I played it, I can't hear anything at all (I'm thirty)

2. I played it again, this time after waiting for a 22 year old co-worker to be about 5 feet away from the PC.

3. He knew nothing of what I was doing, and instantly got a wierd look on his face and went "What the hell is that noise?".

4. I called over everyone explaining what I read, only one person over 30 claimed to hear it. He said he didn't hear anything as much as feel like he was in an airplane though (pressure on the ear).

So, let's see at what ages this seems to work, and from how far. Here is the deal, adults an tell that "something" is making "some kind of noise" from less than a couple feet away. So play the tone on the site, and go more than lets say 7 feet from the speaker. Teenagers can hear this from very far away I read, while adults from only less than a meter (yard). Creating alternate tones to find a sweet spot for teenagers would be cool.

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Neat find! I'm nearly 25 and can hear it up to about 10 feet away at normal volume provided there isn't much room noise. In high school I had a tiny electronic mosquito repeller that I sometmies would turn on and hide in the classroom. It was great seeing kids looking around with a confused look on their face, and then one would ask "what's that buzzing noise??!" Another thing I've found that some people cannot hear or are not attuned to is TVs. From a few rooms away I usually can hear the vertical refresh frequency that most NTSC TVs produce, and it's a lower frequency than this "ringtone" so it's much easier to hear.

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Being fifteen, I can turn the volume up on my speakers about 1/8th of the way up and be able to hear it from approximately ten or eleven feet away. The tone itself is a very high 'B' note and very unpleasant sounding.

Neat find! I'm nearly 25 and can hear it up to about 10 feet away at normal volume provided there isn't much room noise. In high school I had a tiny electronic mosquito repeller that I sometmies would turn on and hide in the classroom. It was great seeing kids looking around with a confused look on their face, and then one would ask "what's that buzzing noise??!" Another thing I've found that some people cannot hear or are not attuned to is TVs. From a few rooms away I usually can hear the vertical refresh frequency that most NTSC TVs produce, and it's a lower frequency than this "ringtone" so it's much easier to hear.

For the record, the vertical refresh frequency for NTSC TV sets is approximately 15.72 khz, or 15720 hz.

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With my headphones I can clearly hear the buzzing (something like "biiiiiiizzzzzzzz" with high - pitched "beeeeep" every few seconds).

With the speakers that weren't on maximum volume, I could hear the sound from another corner of the room (something like 7 steps away) very clearly, but I could slightly hear it from another room that is about 6 steps away.

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This is pretty cool. I can hear it just fine with my volume pretty low (maybe 2/10) from as far as I can go in this room without leaving it (about 15 feet or so). I'm 25. My 24-year-old friend heard it fine at the same distance and volume. It made him paranoid about not being able to hear pinch-harmonics as he gets older though.

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I can hear it up until about 15 ft and I'm 23. But my dog freaked the hell out and ran out of the room when it started. I think I may put in on my digital recorder to shut dogs up when I'm working out on outages...

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Back in the 1980s, Robert E. Iannini of Information Unlimited wrote about certain applications of ultrasonics in his book Build Your Own Laser, Phaser, Ion Ray Gun and Other Working Space Age Projects. That book is out of print, but the same info is availble in his two Electronic Gadgets for the Evil Genius books. Iannini was considered an "elite" among certain old-school hackers.

Young people, and especially young women are more sensitive to ultrasound than other people. Animals expecially rodents, are extemely sensitive to it, and don't like it I might add that ultrasonic noise can cause headaches, nausa, and a general feeling of irritabilty, so if you're experimenting with ultrasonics and notice these symptoms you know why. You also don't want to have your pets nearby, as it also drives them nuts.

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omfg.. Im 16, i couldnt hear it when my volume was low, i turned it up a bit, still couldnt hear it, i turned it up almost all the way very fast, it hurt, like getting your teeth drilled.. and made me sick to my stomach...